1. Field of the Invention
The present invention relates to a method of operating a transmission system of an automotive vehicle of the four-wheel drive type. The invention also relates to a transmission system operating in this way. It also relates to a vehicle including such a transmission system. Finally, the invention relates to a computer program.
The invention applies to a vehicle equipped with a controlled four-wheel drive transmission system (4×4). The objective of this type of vehicle is to improve characteristics such as mobility, notably on starting, i.e. during the setting in motion of the vehicle, and on clearing obstacles.
2. Description of Related Art
A transmission system of the four-wheel drive type is known in which an electromagnetically controlled mechanical coupling means of a front axle and a rear axle (coupler) can operate according to three states defining three operating modes of the transmission system.                a first transmission mode wherein only a (variable) part of the maximum capacity of torque originating from a torque source (the engine of the automotive vehicle) and intended for the rear axle is in fact transmitted to the rear axle; this first mode, known as “4*4 Automatic” mode, corresponding to a “controlled” coupler, i.e. a coupler control system automatically manages its operation, in particular the quantity of transmitted or transmissible torque,        a second transmission mode wherein the totality of the maximum capacity of torque originating from the torque source and intended for the rear axle is in fact transmitted to the rear axle; this second mode, referred to as “4*4 All-terrain” mode, corresponding to a “closed” coupler, i.e. it is locked in a state defining a fixed value of maximum transmissible torque, the locking preferably being electrical,        a third transmission mode wherein no torque (or a negligible torque) originating from the torque source is transmitted to the rear axle; this third mode, known as “4*2” mode, corresponding to an “open” coupler, i.e. the coupler is de-activated or transmits only a negligible quantity of torque.        
The driver must therefore know the operating state of the 4×4 mode of the vehicle according to his interaction with the 4×4 mode selection button. The vehicle must also be able to communicate certain information to the driver, such as, for example, increased temperature of the 4×4 coupler or failure of the 4×4 system. The system must also be able to verify the compatibility of the conditions of speeds and temperatures applied to the coupler. Thus, a need exists for a man-machine interface (MMI) device to receive and interpret the input of the driver applied to a vehicle equipped with a 4×4 transmission system.
A device is known from the document FR2885427 for monitoring and/or controlling equipment of an automotive vehicle with push-buttons and a touchscreen.
An equipment control button on a dashboard of a motorized vehicle is known from document WO 99/20483.
The object of the invention is to provide a method of operating a transmission system allowing the aforementioned problems to be remedied and improving the operating methods known from the prior art. In particular, the invention proposes an operating method allowing driving convenience to be improved and any discomfort or any doubt on the part of the driver regarding his vehicle to be avoided so that said driver can concentrate on driving.